Introduction

Obstructive sleep apnea is due to the collapsibility of the upper airway during sleep. These collapsible soft tissues when subjected to negative pressure within the upper airway may lead to complete or partial obstruction of the upper airway leading to cessation of breathing, increased sympathetic activity, increased blood pressure and hypoxaemia. Collapse of the upper airway is often multilevel, this can happen at the level of the velopharynx, the base of tongue, and/or the lateral pharyngeal walls. Many patients with obstructive sleep apnea (OSA) have bulky thick lateral pharyngeal walls that contribute to the collapse and obstruction of the upper airway at the velopharyngeal level. These areas of collapse should be addressed, if one is aiming to relieve the patient of the apneas. Hence, upper airway evaluation is crucial in the assessment of the anatomical site of obstruction. The level of collapse can be assessed when the patent is awake, using the Muller maneuver (reverse Valsalva) [1] noted with the fiberoptic flexible naso-pharyngoscopy, or when the patient is induced to sleep using intravenous sedatives, documenting the upper airway collapse right time dynamically; known as drug induced sleep endoscopy (DISE). Many patients with OSA have significant lateral wall collapse; in addition, OSA patients may also have concentric collapse (i.e., circular collapse, both anterior posterior and lateral pharyngeal wall collapse).

There are various surgical techniques that have been described to address the bulky lateral pharyngeal wall muscles that causes the lateral pharyngeal wall collapse in OSA. Cahali [2] first described the lateral pharygoplasty in 2003, the procedure was aimed at addressing the lateral pharyngeal wall collapse in patients with OSA. The procedure entailed deep dissection of the superior constrictor muscles, which might explain why some patients had prolonged dysphagia post-operatively. Pang and Woodson [3] in 2007, in their randomized controlled clinical trial, described the Expansion Sphincter Pharyngoplasty (ESP) which involved the dissection of the palatopharyngeus muscle, with its rotation and securing the muscles supero-latero-anteriorly. Pang et al. [3] demonstrated good encouraging clinical results. This ESP technique was inspired after the Orticochea [4] and the Christel et al. [5] procedures used for cleft palates in the 1960s.

In patients with congenital cleft palate, nasal regurgitation is a significant problem; Orticochea [4] in 1964, described the construction of a dynamic muscle sphincter, using the palatopharyngeus muscle, and apposing them bilaterally superiorly in the midline to close the vleopharynx, for treatment of velopharyngeal incompetence in patients with cleft palates. Christel et al. [5] modified this procedure by isolating the palatopharyngeus muscle bilaterally, apposing them more superiorly and closing the lateral pharyngeal defects using Z-plasty sutures. Utilizing these procedures, the Expansion Sphincter Pharyngoplasty was introduced.

It has been 17 years, since the ESP technique was introduced in 2007, and there has been many scientific papers illustrating the various clinical outcomes after OSA patients had the ESP procedure performed; however, there has been no systematic reviews bringing this evidence together. Hence, it is timely that we present a systemic review of the relevant clinical outcomes that have been published on the Expansion Sphincter Pharyngoplasty since its introduction 17 years ago (see Fig. 1).

Fig. 1
figure 1

PRISMA flow diagram of the search and review process

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Materials and methods

Search strategy

We performed a systematic literature search using six databases, namely Medline, PubMed, Embase, Google Scholar, Cochrane Library and Evidence Based Reviews (from 1 January 2007 to 30 June 2023) databases for clinical outcomes for procedures that included the Expansion Pharyngoplasty, Expansion Sphincter Pharyngoplasty, Functional Expansion Pharyngoplasty and its variants (mainly the modified expansion pharyngoplasty and the functional expansion pharyngoplasty). The overall search strategy using Boolean Operators were utilized and combined search terms and keywords including expansion pharyngoplasty, palate surgery, uvulopalatopharyngoplasty, sleep apnea, obstructive sleep apnea, radiological review, heart effects, blood pressure, ophthalmology effects, CPAP, and clinical outcomes.

The PICOT framework was used to aid in the process. Patients—selected in these studies were above 18 years of age. Intervention—the OSA patients who had the Expansion Pharyngoplasty done. Comparison—other various outcome measures were made for these studies, as the AHI is not the most ideal nor holistic. Objective—this was to describe the newer and more holistic and comprehensive clinical outcome measures that were published in the medical literature. Time frame—this was assessed over the past 17 years.

Selection criteria

Study eligibility criteria included ESP for OSA, ≥ 5-year follow-up, with specified outcomes reported. All relevant studies published between 1 January 2007 and 30 June 2023 were included. All included studies had to be published in English and may or may not have some form of comparison with the traditional treatment method for obstructive sleep apnea. We also included adult and pediatric studies. All relevant studies were screened from their abstracts and full articles were obtained and reviewed by all senior co-authors, K.P.P, R.C.T.C, P.M.B, P.G, J.K.S and B.R. There were disagreements noted in the selection of these articles.

Surgical technique

The Expansion Sphincter Pharyngoplasty (ESP) procedure was first introduced by Pang et al. in 2007 [3]. They had described the procedure beginning with a careful bilateral tonsillectomy (without breaching or injuring the underlying palatopharyngeus muscle), followed by identification and isolation of the palatopharyngeus muscle, the lower inferior end of the palatopharyngeus muscle is then incised horizontally (with the electro-cautery or cold dissection) and mobilize this muscle forward and anteriorly. This palatopharyngeus muscle rotation flap is then rotated antero-supero-laterally with a Fig. 8 suture, through the muscle bulk itself, using a vicryl 4/0 round body needle.

This palatopharyngeus muscle is carefully dissected, with intention to leave some muscle fibres with its posterior fascia surface partially attached to the posterior horizontal superior and middle pharyngeal constrictor muscles (this is done intentionally to enhance the tension and “pull” required to create the lateral and superior vector force during the suturing of the muscle down antero-superiorly). Bearing in mind that sufficient muscle bulk has to be isolated to mobilize the muscle and allow the suturing of the muscle with the vicryl suture. The original description (2007, Pang et al) had a supero-lateral incision made on the anterior surface of the anterior tonsillar pillar arch bilaterally, identifying the arching fibers of the palatoglossus muscles. The palatopharyngeus muscle is then attached to these arching fibers of the soft palate anteriorly with a Fig. 8 suture, through the muscle bulk itself, using a vicryl 4/0 round body needle. The direction of the suture and tightening of the suture is toward the direction of the ipsilateral hook of hamulus (one may locate the hook of hamulus, using the index finger and palpating behind the soft palate on the ipsilateral side). A partial uvulectomy may/may not be performed depending on the size and bulk of the uvula (a neo-uvula may be constructed). The anterior and posterior tonsillar pillars are then apposed with vicryl sutures (this is optional).

There have been modifications of the expansion pharyngoplasty technique, namely the Functional Expansion Pharyngoplasty [6, 7] and the Modified Expansion Pharyngoplasty [8], both being fundamentally alike (with the crucial isolation of the palatopharyngeus muscle and its rotation antero-supero-laterally). Both these techniques describe the use of a tunneling method of mobilizing the palatopharyngeus muscle antero-supero-laterally through an incision made on the anterior surface of the soft palate, just medial to the last upper molar on their respective sides.

Data extraction

For studies that met the inclusion criteria, data was extracted into a standardized worksheet. Extracted data included the name of the first author, year of publication, study design, number of study subjects in each treatment group, the age and gender of subjects, the description of the surgical procedure, pre-operative and post-operative AHI, clinical outcomes and their success rates.

The clinical outcome chosen was based on that specific respective scientific paper’s objective and data illustrated. Data collected included pre-operative and post-operative Apnea Hypopnea Index (AHI) values (if available) following the expansion sphincter pharyngoplasty (ESP) and its variants (as mentioned), with the surgical success rate defined as a reduction of post-operative AHI by 50% (compared to pre-operative AHI) and an AHI value below 20. Other outcome measures (if available) included the pre-operative and post-operative Epworth Sleepiness Scale (ESS) and the Snoring Visual Analogue Scale (VAS).

Results

The database search identified twelve studies eligible for analysis (Table 1) [9–20]. Twelve studies were included in this systematic review with a total of 1,373 patients who had the ESP procedure and/or variants of the expansion technique performed (as mentioned in the methodology) and with their relevant clinical outcome data presented (Table 1). These twelve studies illustrated various different outcome parameters after the ESP had been performed, this ranged from radiological reviews, heart effects, blood pressure changes, ophthalmologic effects, CPAP benefits, and clinical outcomes.

Table 1 Showing various clinical outcomes after ESP surgery
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Pang et al. [9] performed a 15-year meta-analysis of sixteen articles with 747 patients who had the ESP procedure done. They reported a mean age of 41.3 years, mean BMI 28.2, with mean pre-op AHI 32.3 and post-op AHI 10.0 (p < 0.05), the mean pre-op ESS was 11.4, had reduced to post-op 5.3 (p < 0.05), and the mean pre-op snore VAS decreased from 8.7 to 2.9 (p < 0.05), with a mean follow-up time of 9.5 months. The authors illustrated an overall pooled success rate for all the 747 patients was 80.0% and noted that there were no significant reported complications noted in these 16 studies.

Fiorella et al. [10] in 2023, compared the efficacy of CPAP versus the ESP procedure in 184 OSA patients. It is traditionally difficult to compare the CPAP and any surgical procedure, however, by utilizing the mean disease alleviation (MDA) formula, the authors presented good comparable results for the ESP and CPAP therapy. There were 77 patients in the ESP group and 107 patients in the CPAP group. AHI reduction was greater in the CPAP group (p = 0.016); however, mean disease alleviation was similar between both groups (p = 0.076), indicating that ESP is as good as CPAP if not better (as the authors qualified that the CPAP usage in their group was particularly better that the international average). They concluded that the overall treatment efficacy as measured by mean disease alleviation was similar for both groups.

Weidenbecher et al. [11] understood that the contraindication to hypoglossal nerve stimulation (HGNS) included OSA patients with velopharyngeal concentric collapse, their authors circumvented this by performing the ESP surgery on these patients, to “convert” these patients’ velopharyngeal collapse to an anterior–posterior pattern of collapse (proven on drug induced sleep endoscopy, DISE), because it is well-known that the ESP was aimed to treat lateral pharyngeal wall collapse, hence by performing the ESP on patients with circumferential velopharyngeal collapse, the resultant velopharynx would demonstrate an anterior posterior collapse (this was again demonstrated on DISE post-procedure). With these same patients, they could then include them into the hypoglossal nerve stimulation group trial. A total of 20 patients were included in their retrospective chart analysis. All patients who underwent ESP successfully converted their velopharyngeal (VP) collapse from concentric collapse (CCC) to an anterior–posterior collapse pattern (after a follow-up of 6 months) and thus met inclusion criteria for HGNS. After the HGNS was implanted, patients showed a significant reduction of the mean AHI from 53.9 before ESP to 8.2 after ESP/HGNS and a decrease in the Epworth Sleepiness Scale (ESS) from a mean of 13.3 to 5.7. ESP can be effective in eliminating the CCC of the VP thus making patients eligible to be HGNS candidates. The authors concluded that in selected OSA patients, who have multilevel upper airway obstruction with complete concentric VP collapse, the combination of ESP/HGNS insertion should be considered.

Masiyev et al. [12], utilized a novel approach of measuring the oro-pharyngeal area and volume with acoustic pharyngometry, in patients before and after the ESP procedure. They demonstrated in 52 OSA patients after the ESP surgery, their mean AHI decreased from 29.6 ± 16.3 to 18.3 ± 18.1. Minimum cross-sectional area (MCA) increased from 1.1 ± 0.4 to 2.3 ± 0.4 cm2, and total pharyngeal volume (TPV) increased from 21.1 ± 6.9 to 31.7 ± 5.5 cm3. The authors concluded that improvement in the upper airway anatomy by expansion sphincter pharyngoplasty can be clearly demonstrated using acoustic pharyngometry. However, they qualified that the acoustic pharyngometry findings are quite similar in patients with successful and unsuccessful outcomes; therefore, pharyngometry findings may not be totally reliable to predict surgical success; and as there are other physiological processes involved, surgical success cannot be solely attributed to the changes in MCA and TPV.

Ciger et al. [13] investigated a novel idea, to compare the efficiency of the anterior palatoplasty and expansion sphincter pharyngoplasty (APwESP) technique for all patterns of velopharyngeal obstruction (anterior–posterior [APPC], lateral [LPC], and combined circular pharyngeal collapse [CPC]). They reported 31 OSA patients (34.1%) were in APPC group, while 30 (33.0%) OSA patients were in LPC, and 30 (33.0%) OSA patients were in CPC group. Pre-operatively for all patients, the mean AHI was 33.4 ± 13.6, Epworth sleepiness scale (ESS) was 16.5 ± 2.6, and lowest oxygen saturation (LSAT) was determined as 85.5% ± 3.6. They found significant post-operative improvement in all parameters for all patients. Interestingly, the authors found no significant difference in outcome parameters between the groups according to obstruction pattern post-operatively; meaning that the obstruction pattern was not a significant factor for AHI reduction (p = 0.234) and LSAT (p = 0.280). The rate of successful surgery (combined APwESP) (based on Sher’s criteria) for severe obstructive sleep apnea in the APPC group was 72.2%, 88.2% in the LPC group, and 75.0% in the CPC group; the authors concluded that the APwESP works for all forms of velopharyngeal collapse.

Wang et al. [14] and Pang et al. [15] both assessed the effects of ESP in upper airway surgery on the blood pressure (BP) readings pre- and post-operative patients. Wang et al. [14] had 62 OSA patients who had the ESP done, 25 patients were on anti-hypertensives, 37 patients were not yet on anti-hypertensives. Post-operatively mean 24-h BP differed significantly after ESP surgery, with systolic BP and diastolic BP (SBP and DBP) decreasing by 5.3 mmHg and 2.5 mmHg, respectively (p < 0.01). Their mean 24-h SBP and DBP decreased in the medicated group by 10.2 mmHg and 4.6 mmHg, respectively (p < 0.001), and significant decreases during the daytime blood pressure by 8.6 mmHg (SBP), 3.0 mmHg (DBP), and nighttime decreases of 12.3 mmHg (SBP), 7.7 mmHg (DBP) (p < 0.001). In the non-medicated treatment group, 24-h SBP and DBP decreased by 1.9 mmHg and 1.1 mmHg (p < 0.005) with significant decreases in mean nighttime BP values of 3.2 mmHg (SBP) and 1.9 mmHg (DBP) (p < 0.001). Pang et al. [15] also demonstrated similar results with their 112 OSA patients with hypertension. These 112 hypertensive OSA patients on oral anti-hypertensive medications, showed a reduction of SBP from 146 ± 15.3 mm Hg to 122 ± 12.5 mm Hg (p < 0.001), and diastolic blood pressure (DBP) reduction from 91 ± 10.2 mm Hg to 76 ± 7.8 mm Hg (p < 0.001), at a mean of 16.1 months post-operative follow up. There was a decrease in overall BMI from 27.5 ± 3.6 to 25.5 ± 3.0 (p < 0.001); however, based on multivariate analysis, the reduction in SBP and DBP was not affected by this BMI reduction. Moreover, the authors reported that 58 patients (51.8%) did not require their antihypertensive after surgery, meaning their post-operative BP had normalized. Cayir et al. [16] demonstrated 3-year long term results after ESP in 39 OSA patients, mean apnea hypopnea index (AHI) values decreased significantly from 25.2 ± 8.3 to 11.6 ± 6.9 (p = 0.012). There were decreases in ESS from baseline to 6-month and 3 years from 10.4, to 4.4, and 4.4, and snoring VAS scores changed from 8.6 to 1.6 and 1.9 (p < 0.05).

Bilal et al. [17] investigated 60 patients, 10 patients had mild OSA (AHI 5–14), 10 patients had moderate OSA (AHI 15–29), 10 had severe OSA (AHI ≥ 30), and 30 normal patients with AHI < 5 (control group). Their preoperative and post-operative (3 months), IL-6, IL-8, TNFα, and raftlin levels were measured. Preoperatively, the mean raftlin levels were 914.4 ± 62.7 pg/mL for the control group (no OSA), 910.0 ± 42.5 pg/mL in the mild OSA group, 1000.5 ± 63.3 pg/mL in the moderate OSA group, and 1386.3 ± 101.4 pg/mL in the severe OSA group, with moderate and severe groups significantly elevated compared to controls (p < 0.001). The authors demonstrated that pre-operative raftlin levels decreased significantly in all OSA groups compared to 3 months post-operative raftlin levels (p < 0.05). Levels of IL-6, IL-8 and TNFα also followed similar patterns at baseline and after surgical intervention. Binar et al. [18] investigated pre- and post-treatment high-sensitivity C-reactive protein (hs-CRP) level in 23 OSA patients who had ESP done and 28 OSA patients who had CPAP treatment. Serum levels of high-sensitivity CRP (hs-CRP) were analyzed by enzyme-linked immunosorbent assays before and 3 months after treatment. They found that both surgical and CPAP treatments caused significant improvements in the clinical and laboratory parameters. However, only the ESP patients whose postoperative AHI levels improved to final AHI of < 5 had significant decrease in their serum CRP levels (p = 0.028); and they found that the CPAP group and the rest of the patients in the surgery group did not show statistically significant difference in CRP levels after treatment. They concluded that treatment with ESP dose significantly reduce post-surgery CRP levels.

Kaya et al. [19] studied 34 eyes of 34 newly diagnosed OSAS patients. Sleep tests were conducted before surgery and 6 months after the expansion sphincter pharyngoplasty (ESP). The authors studied the retinal nerve fiber layer (RNFL), choroidal thickness (CT), and retinal arteriolar caliber (RAC), their analyses were performed using spectral-domain optical coherence tomography. Intraocular pressure (IOP) and ocular pulse amplitude were performed using the Pascal dynamic contour tonometer. They found a significant improvement in the preoperative and postoperative AHI and LSAT values (p = 0.0001 and p = 0.001, respectively) at 6 months post-surgery. There was no significant difference between the preoperative and postoperative RNFL thicknesses (p > 0.05); however, there was significant reduction in IOP post-operatively after the ESP procedure (p = 0.0001).

Suslu et al. [20] demonstrated that heart rate variability (HRV) is a non-invasive and sensitive method used to evaluate autonomic function of the heart based on specific polysomnographic parameters. The authors investigated 28 OSA patients who had the ESP performed, they showed that the AHI decreased in 22 patients (78.6%) after ESP. The ratio of low-frequency power (LF) to high-frequency power (HF) decreased significantly in the patients with successful surgery and in those whose AHI decreased after surgery (p = 0.02 and p = 0.001, respectively). In terms of the change in the LF/HF ratio, 19 ESP patients post-operatively showed a decrease in sympathetic activity, while 9 had an increase in sympathetic activity after ESP. A decrease in sympathetic activity after ESP was significantly associated with surgical success and a decrease in the AHI (p = 0.033 and p = 0.001, respectively). The authors concluded that ESP is effective in reducing the sympathetic activity post-operatively.

Discussion

As it is common that patients with OSA have lateral pharyngeal wall upper airway collapse, there was a real need for some surgical technique to address this lateral pharyngeal wall collapse; Pang et al. [3] introduced the expansion sphincter pharyngoplasty (ESP). The expansion sphincter pharyngoplasty technique was inspired by and modified from the Orticochea [4] procedure and the lateral pharyngoplasty, described by Cahali [2]. Since its introduction in 2007, Pang et al. [9] had published the 15-year meta-analysis on the ESP success rate (based on Sher’s criteria) at 80%. As the Expansion Pharyngoplasty technique has been utilized for 15 years to date, scientific articles have been published to illustrate its beneficial outcomes not only in terms of AHI; and this paper has exactly this objective to demonstrate its benefits, outside the sole AHI parameter.

Holistically speaking, it is well-accepted that documenting the success rate based on Sher’s criteria of AHI reduction by 50% from pre-operative levels, and AHI less than 20 is inadequate, as the AHI itself has its limitations [21, 22]; hence, most sleep physicians would appreciate that the sole reliance on the AHI is frivolous and outdated. Outcomes measures of any treatment intervention should include parameters that measure and assess end-organ damage, like blood pressure measures, excessive daytime sleepiness, quality of life indices, weight and body mass index (BMI). One such acronym that had been suggested previously include the SLEEPGOAL outcome parameters criterion [21]; these success outcome measures that were found to be more holistic included the Snoring visual analogue scale, Latency of sleep onset, Epworth sleepiness scale, execution time (reflex reaction time), blood Pressure (pre- and post-op), Gross weight reduction, Oxygen saturation duration below 90%, AHI, quality of Life scores (pre- and post-surgery).

This article demonstrates the clinical significance that other parameters can be utilized to investigate the positive outcomes of any surgical procedure (in this particular scientific review for outcomes of ESP) include airway size dimension (area and/or volume), biochemical acute phase reactants (IL-6, IL-8, Raftlin, TNF, CRP), intra-ocular pressure and sympathetic activity.

This review article summarizes the different clinical outcome parameters after the ESP procedure in OSA patients, that have been published over the past 17 years, since the introduction of the ESP. This article not only demonstrates the encouraging outcomes of the ESP procedure, but also illustrates the possibility that there are other better outcome parameters that could be utilized to measure success rates post-surgery for OSA patients. It is also a gentle reminder to sleep physicians that more robust longer-term research is needed to validate the outcomes of any surgical procedure and consider other parameters other than the AHI.

We acknowledge and recognize some possible limitations and short comings of this paper:

  1. (a)

    The numbers are relatively small, and moreover, some centers may have had patients that were lost to follow up.

  2. (b)

    Some of these individual papers, itself, have small sample sizes. Hence, their individual data may not reflect the true effect of the procedure.

  3. (c)

    As with most systemic reviews on surgical procedures, the surgeon performing the procedure, might have a slightly different technique and may contribute to the slight difference in success rates.

  4. (d)

    While the original technique was described by Pang et al. [3] in 2007, there have been many modified techniques illustrated after 2007, and this factor alone might affect the success rates of the procedure. Hence, the modified procedures might be heterogenous.

  5. (e)

    With the original description in 2007 by Pang et al. [3], it was indicated for patients with grade 1–2 tonsils, and lateral pharyngeal wall collapse; some of these articles may not have indicated the individual tonsil size/grade in their patients, hence, there could be some bias noted.

  6. (f)

    Not every center practices the same pre-operative protocols. Some centers might use DISE routinely, where other centers might not. The inclusion of pre-operative DISE might also affect the success rates and surgical outcome.

  7. (g)

    Some of the papers used parameters that are not widely accepted as standard outcome measures, but its description itself is an important introduction to the possibility of utilizing other outcome measures other than the AHI.

  8. (h)

    The authors note one possible comment of the tonsil size and “vitality” of the rotated palatopharyngeus muscle. The first original description of the indication of the ESP by Pang et al. [3] was for lateral wall collapse with small grade 1–2 tonsils, not grade 3–4 tonsils, because based on Friedman clinical staging [23], in patients with grade 3–4 tonsils, tonsillectomy alone has a predicted success rate of 70–80%, hence, the ESP is targeted for patients with small tonsils and lateral wall collapse (due to bulky and thick palatopharyngeus muscles). Hence, in the same vein, rotating these muscles with the antero-lateral and superior tension pull-vector would help to enlarge the velopharynx. Moreover, as the tissues scar and stabilize, the vitality of the muscle is secondary, however, we are aware that the muscular branches from the rich arterial pharyngeal plexus is abundant and adequate to maintain vitality of the palatopharyngeus muscle.

Conclusion

The review article clearly shows that ESP demonstrates sustained improvements in both anatomical and clinical outcomes lasting over 5 + years for OSA treatment. Moreover, most authors would concur that the single AHI parameter is inadequate and falls short of being holistic, other outcome measures are needed to demonstrate positive benefits of any upper airway surgical procedure; this article evidenced that these 17 years of the ESP technique and its modifications for OSA patients, have demonstrated significantly better clinical and statistical outcomes. However, there is still a need for larger RCTs with long-term follow-up to further validate effectiveness and durability.